The Upper Colorado River Basin has a drainage area of about 113,500 square miles in western Colorado, eastern Utah, southwestern Wyoming, northeastern Arizona, and northwestern New Mexico. In the 1980’s and 1990’s, the Upper Colorado River Basin was a study area under of the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) program (Sun and Johnston, 1994; Sun and Weeks, 1991). The objectives of the RASA program for the Upper Colorado River Basin were to provide regional assessments of major aquifer systems by providing quantitative assessments of the occurrence, movement, and availability of water stored in rock formations that underlie the basin/watershed. These assessments included: (1) the classification of stratigraphic sequences into those intervals that constitute aquifers and those that constitute confining beds; and (2) the generation of maps that portrayed the areal extent of aquifers, aquifer thickness, and overburden thickness. These studies generated a large body of subsurface geologic information as part of the regional aquifer analyses, some of which are captured in this digital data release. Aquifer systems in consolidated rocks in the Upper Colorado River Basin have been grouped into three major subdivisions of sedimentary rocks; in descending order: (1) Tertiary-rock aquifers, (2) Mesozoic-rock aquifers, and (3) Paleozoic-rock aquifers (Taylor and others, 1983; 1986). Within each aquifer group, rocks are further divided into aquifers and confining units on the basis of lithology, depositional environment, and hydrologic characteristics (Glover and others, 1998; Freethy and Cordy, 1991; Geldon, 2003). In a report describing consolidated-rock aquifers of Paleozoic age, 7 hydrostratigraphic units were defined, four aquifers and three confining units (Geldon, 2003). The hydrostratigraphic units of Paleozoic age are locally exposed around the margins of uplifts and in deeply-incised canyon; they occur widely in the subsurface of the Upper Colorado River Basin study area, except in parts of the Uinta, Wind River, and Uncompahgre uplifts where they have been removed by erosion. These hydrostratigraphic units are part of the stratigraphic sequence of Paleozoic rocks that has a total thickness of more than 5,000 ft. This digital dataset contains spatial datasets corresponding to the contoured subsurface maps of Paleozoic rock units produced by the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) of the Upper Colorado River Basin (Geldon, 2003). The data define the thickness, extent, nomenclature, and facies characteristics of principal hydrostratigraphic units of Paleozoic age in the basin. The digital data describe the following hydrostratigraphic units: the Flathead aquifer, the Gros Ventre confining unit, the Bighorn aquifer, the Elbert-Parting confining unit, the Madison aquifer (consisting of two zones, the Redwall-Leadville zone, and the Darwin-Humbug zone), the Four Corners confining unit (consisting of the Belden-Molas subunit and the Paradox-Eagle Valley subunit), and the Canyonlands aquifer (consisting of three zones, the Cutler-Maroon zone, the Weber-de Chelly zone, and the Park City-State Bridge zone). Contoured thickness and lithology data for each unit are contained in line features classes within a geodatabase; unit extents, facies extents, and formation nomenclatural extents are represented as polygon feature classes. Both types of data are also saved as individual shapefiles. Nonspatial tables define the data sources used, terminology, and the stacking hierarchy and component geologic formations of each the of hydrostratigraphic units

The Upper Colorado River Basin has a drainage area of about 113,500 square miles in western Colorado, eastern Utah, southwestern Wyoming, northeastern Arizona, and northwestern New Mexico. In the 1980’s and 1990’s, the Upper Colorado River Basin was a study area under of the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) program (Sun and Johnston, 1994; Sun and Weeks, 1991). The objectives of the RASA program for the Upper Colorado River Basin were to provide regional assessments of major aquifer systems by providing quantitative assessments of the occurrence, movement, and availability of water stored in rock formations that underlie the basin/watershed. These assessments included: (1) the classification of stratigraphic sequences into those intervals that constitute aquifers and those that constitute confining beds; and (2) the generation of maps that portrayed the areal extent of aquifers, aquifer thickness, and overburden thickness. These studies generated a large body of subsurface geologic information as part of the regional aquifer analyses, some of which are captured in this digital data release. Aquifer systems in consolidated rocks in the Upper Colorado River Basin have been grouped into three major subdivisions of sedimentary rocks; in descending order: (1) Tertiary-rock aquifers, (2) Mesozoic-rock aquifers, and (3) Paleozoic-rock aquifers (Taylor and others, 1983; 1986). Within each aquifer group, rocks are further divided into aquifers and confining units on the basis of lithology, depositional environment, and hydrologic characteristics (Glover and others, 1998; Freethy and Cordy, 1991; Geldon, 2003). In a report describing consolidated-rock aquifers of Mesozoic age, 10 hydrostratigraphic units were defined, five aquifers and five confining units (Freethy and Cordy, 1991). The hydrostratigraphic units of Mesozoic age occur throughout the Upper Colorado River Basin study area, except in parts of the Uinta, White River, and San Juan uplifts where they have been removed by erosion. These hydrostratigraphic units are part of the stratigraphic sequence of Mesozoic rocks that has a total thickness of more than 8,000 ft. The sandstones of Mesozoic age are the most areally extensive and the thickest bedrock aquifers in the Upper Colorado River Basin. This digital dataset contains spatial datasets corresponding to the contoured subsurface maps produced by the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) of the Upper Colorado River Basin (Freethy and Cordy, 1991). The data define the thickness and extent of principal hydrostratigraphic units of Mesozoic age in the basin. The digital data describe the following hydrostratigraphic units: the Chinle-Moenkopi confining unit, the Navajo-Nugget aquifer, the Carmel-Twin Creek confining unit, the Entrada-Preuss aquifer, the Curtis-Stump confining unit, the Morrison aquifer, the Morrison confining unit, the Dakota aquifer, the Mancos confining unit, and the Mesaverde aquifer. Contoured thickness data for each unit are contained in line features classes within a geodatabase; unit extents are represented as polygon feature classes. Both types of data are also saved as individual shapefiles. Nonspatial tables define the data sources used, and the stacking hierarchy and component geologic formations of each the of hydrostratigraphic units.

The Upper Colorado River Basin has a drainage area of about 113,500 square miles in western Colorado, eastern Utah, southwestern Wyoming, northeastern Arizona, and northwestern New Mexico. In the 1980’s and 1990’s, the Upper Colorado River Basin was a study area under of the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) program (Sun and Johnston, 1994; Sun and Weeks, 1991). The objectives of the RASA program for the Upper Colorado River Basin were to provide regional assessments of major aquifer systems by providing quantitative assessments of the occurrence, movement, and availability of water stored in rock formations that underlie the basin/watershed. These assessments included: (1) the classification of stratigraphic sequences into those intervals that constitute aquifers and those that constitute confining beds; and (2) the generation of maps that portrayed the areal extent of aquifers, aquifer thickness, and overburden thickness. These studies generated a large body of subsurface geologic information as part of the regional aquifer analyses, some of which are captured in this digital data release. Aquifer systems in consolidated rocks in the Upper Colorado River Basin have been grouped into three major subdivisions of sedimentary rocks; in descending order: (1) Tertiary-rock aquifers, (2) Mesozoic-rock aquifers, and (3) Paleozoic-rock aquifers (Taylor and others, 1983; 1986). Within each aquifer group, rocks are further divided into aquifers and confining units on the basis of lithology, depositional environment, and hydrologic characteristics (Glover and others, 1998; Freethy and Cordy, 1991; Geldon, 2003). In a report describing consolidated-rock aquifers of Mesozoic age, 10 hydrostratigraphic units were defined, five aquifers and five confining units (Freethy and Cordy, 1991). The hydrostratigraphic units of Mesozoic age occur throughout the Upper Colorado River Basin study area, except in parts of the Uinta, White River, and San Juan uplifts where they have been removed by erosion. These hydrostratigraphic units are part of the stratigraphic sequence of Mesozoic rocks that has a total thickness of more than 8,000 ft. The sandstones of Mesozoic age are the most areally extensive and the thickest bedrock aquifers in the Upper Colorado River Basin. This digital dataset contains spatial datasets corresponding to the contoured subsurface maps produced by the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) of the Upper Colorado River Basin (Freethy and Cordy, 1991). The data define the thickness and extent of principal hydrostratigraphic units of Mesozoic age in the basin. The digital data describe the following hydrostratigraphic units: the Chinle-Moenkopi confining unit, the Navajo-Nugget aquifer, the Carmel-Twin Creek confining unit, the Entrada-Preuss aquifer, the Curtis-Stump confining unit, the Morrison aquifer, the Morrison confining unit, the Dakota aquifer, the Mancos confining unit, and the Mesaverde aquifer. Contoured thickness data for each unit are contained in line features classes within a geodatabase; unit extents are represented as polygon feature classes. Both types of data are also saved as individual shapefiles. Nonspatial tables define the data sources used, and the stacking hierarchy and component geologic formations of each the of hydrostratigraphic units.

This data release presents geologic map data for the bedrock geology of the Aztec 1-degree by 2-degree quadrangle, New Mexico. Geologic mapping incorporates new interpretive contributions and compilation from published geologic map data sources primarily ranging from 1:24,000 to 1:50,000 scale. Much of the geology incorporated from published geologic maps is adjusted based on digital elevation model and natural-color image data sources to improve spatial resolution of the data. Spatial adjustments and new interpretations also eliminate mismatches at source map boundaries. This data set represents only the bedrock geology; deposits of unconsolidated, surficial materials that are typically, but not exclusively, Quaternary in age, are not included in this database. Bedrock in the context of this database includes all metamorphic, sedimentary, and igneous rocks regardless of age. Bedrock geology is continuous to the extent that map units and structures can be appropriately constrained, including throughout areas overlain by surficial deposits. Line features that are projected through areas overlain by surficial deposits are generally attributed with lower identity and existence confidence, larger locational confidence values, and a compilation method in the MethodID field indicating features were projected beneath cover (see Turner and others [2022] for a description of MethodID field). Map units represented in this database range from Paleoproterozic and Mesoproterozic metamorphic and intrusive rocks to Pliocene and Quaternary sedimentary and volcanic rocks. Map units and structures in this data set reflect multiple events that are significant at regional and continental scales including multiple Proterozoic accreted terranes, magmatic episodes, supracrustal depositional environments, and continental margin environments, Ancestral Rocky Mountains, Laramide orogeny, Southern Rocky Mountains volcanism, and Rio Grande rift in the Phanerozoic. Map units are organized within geologic provinces as described by the Seamless Integrated Geologic Mapping (SIGMa) (Turner and others, 2022) extension to the Geologic Map Schema (GeMS) (USGS, 2020). Geologic provinces are used to organize map units based on time-dependent, geologic events rather than geographic or rock type groupings that are typical of traditional geologic maps. The detail of geologic mapping is approximately 1:100,000-scale depending on the scale of published geologic maps and new mapping based on field observations or interpretation from basemap data. The database follows the schema and structure of SIGMa (Turner and others, 2022) that is an extension to GeMS (USGS, 2020). Turner, K.J., Workman, J.B., Colgan, J.P., Gilmer, A.K., Berry, M.E., Johnstone, S.A., Warrell, K.F., Dechesne, M., VanSistine, D.P., Thompson, R.A., Hudson, A.M., Zellman, K.L., Sweetkind, D., and Ruleman, C.A., 2022, The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS): U.S. Geological Survey Scientific Investigations Report 2022–5115, 33 p., https://doi.org/ 10.3133/ sir20225115. U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema)-A standard format for the digital publication of geologic maps: U.S. Geological Survey Techniques and Methods, book 11, chap. B10, 74 p., https://doi.org/10.3133/tm11B10.

This data release presents geologic map data for the bedrock geology of the Aztec 1-degree by 2-degree quadrangle, New Mexico. Geologic mapping incorporates new interpretive contributions and compilation from published geologic map data sources primarily ranging from 1:24,000 to 1:50,000 scale. Much of the geology incorporated from published geologic maps is adjusted based on digital elevation model and natural-color image data sources to improve spatial resolution of the data. Spatial adjustments and new interpretations also eliminate mismatches at source map boundaries. This data set represents only the bedrock geology; deposits of unconsolidated, surficial materials that are typically, but not exclusively, Quaternary in age, are not included in this database. Bedrock in the context of this database includes all metamorphic, sedimentary, and igneous rocks regardless of age. Bedrock geology is continuous to the extent that map units and structures can be appropriately constrained, including throughout areas overlain by surficial deposits. Line features that are projected through areas overlain by surficial deposits are generally attributed with lower identity and existence confidence, larger locational confidence values, and a compilation method in the MethodID field indicating features were projected beneath cover (see Turner and others [2022] for a description of MethodID field). Map units represented in this database range from Paleoproterozic and Mesoproterozic metamorphic and intrusive rocks to Pliocene and Quaternary sedimentary and volcanic rocks. Map units and structures in this data set reflect multiple events that are significant at regional and continental scales including multiple Proterozoic accreted terranes, magmatic episodes, supracrustal depositional environments, and continental margin environments, Ancestral Rocky Mountains, Laramide orogeny, Southern Rocky Mountains volcanism, and Rio Grande rift in the Phanerozoic. Map units are organized within geologic provinces as described by the Seamless Integrated Geologic Mapping (SIGMa) (Turner and others, 2022) extension to the Geologic Map Schema (GeMS) (USGS, 2020). Geologic provinces are used to organize map units based on time-dependent, geologic events rather than geographic or rock type groupings that are typical of traditional geologic maps. The detail of geologic mapping is approximately 1:100,000-scale depending on the scale of published geologic maps and new mapping based on field observations or interpretation from basemap data. The database follows the schema and structure of SIGMa (Turner and others, 2022) that is an extension to GeMS (USGS, 2020). Turner, K.J., Workman, J.B., Colgan, J.P., Gilmer, A.K., Berry, M.E., Johnstone, S.A., Warrell, K.F., Dechesne, M., VanSistine, D.P., Thompson, R.A., Hudson, A.M., Zellman, K.L., Sweetkind, D., and Ruleman, C.A., 2022, The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS): U.S. Geological Survey Scientific Investigations Report 2022–5115, 33 p., https://doi.org/ 10.3133/ sir20225115. U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema)-A standard format for the digital publication of geologic maps: U.S. Geological Survey Techniques and Methods, book 11, chap. B10, 74 p., https://doi.org/10.3133/tm11B10.

The San Juan basin is a significant physical and structural element in the southeastern part of the Colorado Plateau physiographic province. The San Juan basin is in New Mexico, Colorado, Arizona, and Utah and has an area of about 21,600 square miles. The basin is about 140 miles wide and about 200 miles long. In the 1980’s and 1990’s, the San Juan basin was the focus of the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) study. Investigation of the San Juan structural basin began in October 1984 with an objective, among others, to define and evaluate the aquifer system. As part of this analysis, a multi-publication series of reports were produced as Hydrologic Atlas 720 (HA-720) that described on 1:1,000,000-scale maps the subsurface configuration and hydrogeology of the San Jose, Nacimiento, and Animas Formations (Levings and others, 1990; HA-720-A), the Ojo Alamo Sandstone (Thorn and others, 1990; HA-720-B), the Kirtland Shale and Fruitland Formation (Kernodle and others, 1990; HA-720-C), the Pictured Cliffs Sandstone (Dam and others, 1990; HA-720-D), the Cliff House Sandstone (Thorn and others, 1990; HA-720-E), the Menefee Formation (Levings and others, 1990; HA-720-F), the Point Lookout Sandstone (Craigg and others, 1990; HA-720-G), the Gallup Sandstone (Kernodle and others, 1990; HA-720-H), the Dakota Sandstone (Craigg and others, 1990; HA-720-I), and the Morrison Formation (Dam and others, 1990; HA-720-J). This digital dataset contains spatial datasets corresponding to the contoured subsurface maps produced by the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) San Juan basin study. The data define the elevation, thickness, and extent of principal stratigraphic units of the basin. The digital data describe the following stratigraphic units: the San Jose Formation, the Ojo Alamo Sandstone, the Kirtland Shale and Fruitland Formation, the Pictured Cliffs Sandstone, the Cliff House Sandstone, the Menefee Formation, the Point Lookout Sandstone, the Gallup Sandstone, the Dakota Sandstone, and the Morrison Formation. Digital data for each unit are contained in individual features classes within a geodatabase (also saved as individual shapefiles). Feature classes have a single attribute, either elevation or thickness, that represents the contoured value. Contoured values are given in feet, to maintain consistency with the original publication, and in meters.

The San Juan basin is a significant physical and structural element in the southeastern part of the Colorado Plateau physiographic province. The San Juan basin is in New Mexico, Colorado, Arizona, and Utah and has an area of about 21,600 square miles. The basin is about 140 miles wide and about 200 miles long. In the 1980’s and 1990’s, the San Juan basin was the focus of the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) study. Investigation of the San Juan structural basin began in October 1984 with an objective, among others, to define and evaluate the aquifer system. As part of this analysis, a multi-publication series of reports were produced as Hydrologic Atlas 720 (HA-720) that described on 1:1,000,000-scale maps the subsurface configuration and hydrogeology of the San Jose, Nacimiento, and Animas Formations (Levings and others, 1990; HA-720-A), the Ojo Alamo Sandstone (Thorn and others, 1990; HA-720-B), the Kirtland Shale and Fruitland Formation (Kernodle and others, 1990; HA-720-C), the Pictured Cliffs Sandstone (Dam and others, 1990; HA-720-D), the Cliff House Sandstone (Thorn and others, 1990; HA-720-E), the Menefee Formation (Levings and others, 1990; HA-720-F), the Point Lookout Sandstone (Craigg and others, 1990; HA-720-G), the Gallup Sandstone (Kernodle and others, 1990; HA-720-H), the Dakota Sandstone (Craigg and others, 1990; HA-720-I), and the Morrison Formation (Dam and others, 1990; HA-720-J). This digital dataset contains spatial datasets corresponding to the contoured subsurface maps produced by the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) San Juan basin study. The data define the elevation, thickness, and extent of principal stratigraphic units of the basin. The digital data describe the following stratigraphic units: the San Jose Formation, the Ojo Alamo Sandstone, the Kirtland Shale and Fruitland Formation, the Pictured Cliffs Sandstone, the Cliff House Sandstone, the Menefee Formation, the Point Lookout Sandstone, the Gallup Sandstone, the Dakota Sandstone, and the Morrison Formation. Digital data for each unit are contained in individual features classes within a geodatabase (also saved as individual shapefiles). Feature classes have a single attribute, either elevation or thickness, that represents the contoured value. Contoured values are given in feet, to maintain consistency with the original publication, and in meters.

This digital data release presents subsurface data from multiple geologic units that were part of a previous study of the regional subsurface structural configuration of the Powder River Basin in Wyoming and Montana. The original data within this geodatabase is sourced from an unpublished doctoral dissertation by Jessie Melick at Montana State University (Melick, 2013). Data contained in this release were generated from elevation grids developed by Jessie Melick using 28,000 wells and geophysical well logs penetrating Paleozoic to Mesozoic strata over a 70,000 square-kilometer area designated by the Department of Energy as a realistic locality for geologic carbon sequestration (Melick, 2013). Information included in this release represents a small component of the larger geomodel, which includes rock-property details such as facies analysis, porosity calculations, and net to gross thickness, among others. Well locations, well identification numbers, geophysical logs, and any other non-public data or information used in the creation of this dataset has been explicitly omitted. Data in this release includes elevation point features on the stratigraphic tops of the Mesaverde Group, Frontier Formation, Lakota Formation, Tensleep Formation, Madison Group, and Precambrian basement that were exported from the original horizon grids as points on a 500x500 m grid spacing. This release additionally contains structure contour maps of the tops of these same units; the contours were digitally generated from the point arrays using automated contouring methods within a geographic information system. Characterizing these units in the subsurface is of value, as they have been identified as potential reservoirs for the geologic sequestration of carbon, units of interest for geothermal energy production, may serve as regional groundwater aquifers, and are currently considered productive hydrocarbon reservoirs (Melick, 2013). Formation top points and structure contours were formatted and attributed as GIS data sets for use in digital form as part of U.S. Geological Survey’s ongoing effort to inventory, catalog, and release subsurface geologic data in geospatial form. This effort is part of a broad directive to develop 2D and 3D geologic information at detailed, national, and continental scales. This data approximates, but does not strictly follow the USGS NCGMP GeMS data structure schema for geologic maps.Structure contour lines for each formation are stored within separate “IsoValueLine” feature classes, while formation tops for each formation are stored as point data in separate “MapUnitPoints” feature classes. These are distributed within a geographic information system geodatabase and are also saved as shapefiles. Contour and point data are provided in both feet and meters to maintain consistency with the original publication and for ease of use. Nonspatial tables define the data sources used, define terms used in the dataset, and describe the geologic units referenced herein. A tabular data dictionary describes the entity and attribute information for all attributes of the geospatial data and accompanying nonspatial tables.

This digital data release presents subsurface data from multiple geologic units that were part of a previous study of the regional subsurface structural configuration of the Powder River Basin in Wyoming and Montana. The original data within this geodatabase is sourced from an unpublished doctoral dissertation by Jessie Melick at Montana State University (Melick, 2013). Data contained in this release were generated from elevation grids developed by Jessie Melick using 28,000 wells and geophysical well logs penetrating Paleozoic to Mesozoic strata over a 70,000 square-kilometer area designated by the Department of Energy as a realistic locality for geologic carbon sequestration (Melick, 2013). Information included in this release represents a small component of the larger geomodel, which includes rock-property details such as facies analysis, porosity calculations, and net to gross thickness, among others. Well locations, well identification numbers, geophysical logs, and any other non-public data or information used in the creation of this dataset has been explicitly omitted. Data in this release includes elevation point features on the stratigraphic tops of the Mesaverde Group, Frontier Formation, Lakota Formation, Tensleep Formation, Madison Group, and Precambrian basement that were exported from the original horizon grids as points on a 500x500 m grid spacing. This release additionally contains structure contour maps of the tops of these same units; the contours were digitally generated from the point arrays using automated contouring methods within a geographic information system. Characterizing these units in the subsurface is of value, as they have been identified as potential reservoirs for the geologic sequestration of carbon, units of interest for geothermal energy production, may serve as regional groundwater aquifers, and are currently considered productive hydrocarbon reservoirs (Melick, 2013). Formation top points and structure contours were formatted and attributed as GIS data sets for use in digital form as part of U.S. Geological Survey’s ongoing effort to inventory, catalog, and release subsurface geologic data in geospatial form. This effort is part of a broad directive to develop 2D and 3D geologic information at detailed, national, and continental scales. This data approximates, but does not strictly follow the USGS NCGMP GeMS data structure schema for geologic maps.Structure contour lines for each formation are stored within separate “IsoValueLine” feature classes, while formation tops for each formation are stored as point data in separate “MapUnitPoints” feature classes. These are distributed within a geographic information system geodatabase and are also saved as shapefiles. Contour and point data are provided in both feet and meters to maintain consistency with the original publication and for ease of use. Nonspatial tables define the data sources used, define terms used in the dataset, and describe the geologic units referenced herein. A tabular data dictionary describes the entity and attribute information for all attributes of the geospatial data and accompanying nonspatial tables.

This digital data release contains geospatial geologic and paleontological data of the 1° x2 °, 1:250,000 Limon quadrangle covering eastern Colorado and western Kansas. The dataset is a digital reproduction of previously published U.S. Geological Survey field mapping which illustrates the spatial configuration of primarily Quaternary surficial units overlying upper Miocene, Oligocene, Paleocene, and Upper Cretaceous bedrock (Sharps, 1980). This quadrangle contains numerous outcrop of the Ogallala Formation, which is a prolific freshwater aquifer throughout the broader great plains. A structure contour map of the top of the Dakota Sandstone are included, which was constructed using selected oil and gas well logs (Sharps, 1980). The Dakota Sandstone is a productive hydrocarbon reservoir within the Limon quadrangle, and the broader Denver-Julesburg Basin. Point data for Mesozoic invertebrate fossil collection localities are depicted on the map, depicted with either Denver or Washington D.C. U.S. Geological Survey catalog numbers (Sharps, 1980). The digital geologic database presented here is an accurate replication of original US. Geological Survey mapping in the Limon quadrangle (Sharps, 1980). Geologic map polygons, fossil points, faunal zones, and structure contours were digitized and attributed as GIS data sets as part of the U.S. Geological Survey’s ongoing studies on a regional and national scale. The geologic map polygons, fossil point features, faunal zone lines, and structure contour lines are distributed as separate feature classes within a geographic information system geodatabase. Contoured elevation values are given in feet, to maintain consistency with the original publication, and in meters. Nonspatial tables define the data sources used, define terms used in the dataset, and describe the geologic units. A tabular data dictionary describes the entity and attribute information for all attributes of the geospatial data and the accompanying nonspatial tables.